Tubular structure agglomerates of calcium carbonate crystals formed on a cation-exchange membrane

Crystallization of calcium carbonate was carried out by using 1 M calcium chloride and 1 M sodium carbonate and a specially designed crystallizer equipped with a cation-exchange membrane. The crystallizer is a jacketed cylindrical glass tube that was divided into two compartments by a cation-exchange membrane and placed horizontally. Calcium carbonate crystals grew on the surface of the cation-exchange membrane in the sodium carbonate solution side and formed self-assembled tubular agglomerates vertically against the membrane surface. The tube was named the CC-tube. The inner and outer diameters of the CC-tube obtained after 9 days of crystallization at 50 degrees C was about 15 and 30 mu m, respectively. The length was about 200-400 mu m. Most of the CC-tubes were composed of small calcite crystals. The growing site of the tube was concluded to be the interface between the membrane and the tube rather than the top of tube.